Colonic drug delivery formulation

ABSTRACT

A delayed release coating comprising a mixture of a first material selected from starch; amylose; amylopectin; chitosan; chondroitin sulfate; cyclodextrin; dextran; pullulan; carrageenan; scleroglucan; chitin; curdulan and levan, and a second material which has a pH threshold at about pH 5 or above, is used to target release of a drug from a core to the intestine, particularly the colon

The present invention relates to a delayed release formulation with a core comprising a drug and a delayed release coating. In particular, it relates to a delayed release formulation for a drug for delivering to the colon.

The targeting of drugs to the colon can be utilised as a means of achieving local therapy or systemic treatment. The colon is susceptible to a number of disease states, including inflammatory bowel disease, irritable bowel syndrome, constipation, diarrhoea, infection and carcinoma. In such conditions, drug targeting to the colon would maximise the therapeutic effectiveness of the treatment. The colon can also be utilised as a portal for the entry of drugs into the systemic circulation. Various formulations have been developed for colonic drug delivery, including pro-drugs as well as formulated dosage forms, with the latter being more popular since the concept once proved can be applied to other drugs.

The higher bacterial population in the colon has- also been exploited in developing colonic drug delivery dosage forms through the use, as carrier materials, of naturally occurring complex polysaccharides that constitute substrates for the numerous enzymes of the resident colonic bacteria. These materials are able to pass through the upper gastrointestinal regions intact but are digested upon entry into the colon. Those studied so far include amylose, pectin, chitosan, galactomannan etc. In at least its amorphous form, amylose is resistant to digestion by the enzymes of the upper gastrointestinal tract. It is however fermented in the colon by ∝-amylase enzymes produced by over half of the 400 bacteria species resident in the colon.

One major attraction of using polysaccharide in this bacterial enzyme approach to colonic drug delivery is that materials used are of food grade and so would be safe for use in humans. They are usually applied as coatings or incorporated in the core material as a matrix carrier, and their digestion on entry into the colon by the colonic bacterial enzymes leads to the release of the drug load. An example of such a formulation, which employs an amylose coating, is disclosed in EP 0 343 993 (BTG International Limited).

A major limitation with these naturally occurring materials however is that they swell excessively in aqueous media leading to leaching of the drug load in the upper gastrointestinal regions. To circumvent this problem, they have been utilised in a mixture with impermeable materials (e.g. amylose is mixed with the water-insoluble polymer ethylcellulose). However, the problem with such modifications/mixtures is in finding the right balance between hydrophobicity and hydrophilicity that would prevent inopportune drug release in the upper gastrointestinal regions, but which would also at the same time permit enzyme access to the polysaccharide substrate and ensure drug release at an adequate rate.

An attempt to solve the problem of the excessive swelling of amylose is disclosed in EP 0 502 032 (British Technology Group Ltd). This employs an outer coating comprising a film forming cellulose or acrylic polymer material and amorphous amylose for a tablet comprising an active compound. One embodiment has the active compound coated first with an inner coating of amylose and then a separate outer coating of the cellulose or acrylic polymer material. Another embodiment has an outer coating which is an admixture of amylose and a cellulose or acrylic polymer. The reference makes clear that the degradation of the cellulose materials in vivo is in general not pH dependent and it is preferred that this is also true for the acrylate materials. Every example disclosed in the reference is of a pH independent cellulosic or acrylic polymer.

An article in Journal of Controlled Release 38 (1996) 75-84 (Milojevic et al) investigates the incorporation of a range of insoluble polymers into an amylose coating in order to control amylose swelling. A range of cellulose and acrylate based co-polymers are assessed, and a commercially available ethyl cellulose (Ethocel®) is found to control the swelling most effectively. Another single layer coating that is investigated is a mixture of amylose and two pH independent acrylic polymers, namely Eudragit® RS and RL, but this coating is found not to give such effective results. A pH dependent soluble coating of Eudragit® L100 is employed but only in a multi-layer system comprising a bioactive coated with an inner coating of amylose and then an outer coating of Eudragit® L100.

A further amylose-based coating composition is disclosed in WO 99/21536 (BTG International Limited). The coating composition comprises a mixture of amylose and a water insoluble film-forming polymer which is formed from a water-insoluble cellulosic or acrylic polymer material. As with EP 0 502 032, it is made clear that degradation of the cellulose materials in vivo is in general not pH dependent and it is preferred that this is also true for the acrylate materials. It would appear that the PCT specification contains a typographical error, because it goes on to say that a preferred form of acrylate material is “Eudragit L whose degradation is independent of pH”. It is believed that this should refer to “Eudragit RL” whose degradation is indeed independent of pH. It cannot be intended to refer to Eudragit L, as the degradation of this polymer is pH dependent.

WO 99/25325 (BTG International Limited) also discloses a delayed release coating comprising amylose and (preferably) ethyl cellulose or alternatively an acrylate polymer the degradation of which is independent of pH. The coating composition also includes a plasticiser and the method finds particular application in the preparation of dosage forms comprising active materials that are unstable at temperatures in excess of 60° C., as the composition is formed at lower temperatures than this. It should be noted that this reference also includes the typographical error relating to Eudragit L described above.

WO 03/068196 (Alizyme Theraputics Ltd) discloses a specific delayed release coating for the bioactive prednisolone solium metasulphobenzoate comprising glassy amylose, ethyl cellulose and dibutyl sebacate.

The use of polysaccharides other than amylose in a delayed release coating is disclosed in GB 2 367 002 A (British Sugar PLC). Examples include guar gum, karaya gum, gum tragacanth and xanthan gum. Microparticles of these polysaccharides are dispersed in a water-insoluble film-forming polymer matrix formed for example from a cellulose derivative, an acrylic polymer or a lignin.

WO 01/76562 (Tampereen Patenttitoimisto Oy) discloses a peroral pharmaceutical formulation containing a drug and a chitosan (a polysaccharide obtained from chitin) for controlling its release. The drug and the chitosan are mixed into a homogeneous mechanical powder mixture which is granulated and then optionally tabletised. The granulation may be performed with an enteric polymer (such as a coploymer of methacrylic acid) or the granules may be provided with a porous enteric coating.

WO 2004/052339 (Salvona LLC) discloses a pH dependent drug release system which is a free-flowing powder of solid hydrophobic nano-spheres comprising a drug encapsulated in a pH-sensitive micro-sphere. The nano-spheres are formed from the drug in combination with a wax material, and the pH-sensitive micro-sphere formed from a pH-sensitive polymer (such as a Eudragit® polymer) in combination with a water-sensitive material such as a polysaccharide. The present applicant believes however that the very small particle sizes involved in this reference would not in practice delay the release of the bioactive core.

In accordance with a first aspect of the present invention, there is provided a delayed release drug formulation comprising a particle with a core and a coating for the core, the core comprising a drug and the coating comprising a mixture of a first material which is susceptible to attack by colonic bacteria (such as amylose) and a second material, the solubility of which is dependent upon pH (such as Eudragit® S), wherein the minimum diameter of the particle is at least 10⁻⁴ m and preferably at least 10⁻³ m. In a particularly preferred embodiment, the particle has a minimum diameter from 0.5 mm to 10 mm, most preferably from 6 to 10 mm.

It has surprisingly been discovered that the disadvantageous swelling of materials such as amylose can be controlled by a pH dependent material. The pH dependent material is preferably an acrylic polymer, and most preferably is Eudragit S®.

A further technical advantage of the present invention (compared for example to the formulation disclosed in WO 01/76562) is that substantially no drug is released for an extended period (that is, whilst the coating is being dissolved), following which the drug is released relatively quickly. This is in contrast to homogeneous tablets from which the drug release profile is gradual from the outset rather than delayed then pulsatile.

The amylose is preferably provided in the form of a high amylose starch, for example Hylon 7 or Eurylon 7 (a starch having about 70% by weight amylose).

The mixture of the first and second materials is preferably substantially homogeneous.

In a preferred embodiment, it has been found that a mix of two polymers at an appropriate ratio, applied as a film coating on to a core, minimises drug release in the stomach and small intestine. Subsequent drug release in the colon occurs by the combined active physiological triggers: preferably by Eudragit® S dissolution and amylose digestion.

The proportion of the first material to the second material may in some circumstances be up to 50:50, preferably up to 65:35 and most preferably from 15:85 to 30:70.

Optionally, conventional excipients such as plasticisers for film formation (for example triethyl citrate) and anti-tack agents (such as glyceryl monostearate) may be included in amounts up to 30% by weight of the final composition.

By saying that the coating comprises a mixture of the first and second materials, it is intended to exclude the known multi-layer dosage form (disclosed for example in Milojevic et al. described above) in which an active core is coated first with an inner coating of amylose and then with an outer coating of Eudragit® L100. Such a multi-layer dosage form does not comprise a mixture of amylose and Eudragit® L100.

The formulation of the present invention may however have an additional layer either between the active core and the layer comprising the delayed release composition of the present invention and/or an outer layer coating the delayed release composition layer.

The composition preferably forms a coating around the bioactive which is most preferably a substantially homogeneous mixture of amylose and Eudragit® S.

In a third aspect of the invention, there is provided a method of targeting a drug to the colon comprising administering to a patient a formulation as defined above.

In a fourth aspect of the invention, there is provided a formulation as defined above for use in a method of medical treatment of the human or animal body by therapy.

In a fifth aspect of the invention, there is provided the use of a formulation as defined above in the manufacture of a medicament for the treatment of inflammatory bowel disease, irritable bowel syndrome, constipation, diarrhoea, ulcerative colitis, infection and cancer.

A number of preferred embodiments of the present invention will now be described with reference to the drawings, in which:-

FIG. 1 shows the dissolution profile of mixed film coated tablets at 5% TWG and Eudragit S coated tablets at 5% TWG in pH 7.0 buffer;

FIG. 2 shows the dissolution profile of mixed film coated tablets as for FIG. 1 but with 6% TWG;

FIG. 3 shows the dissolution profile of mixed film coated tablets as for FIG. 1 but with 7.4% TWG;

FIG. 4 shows the dissolution profile of mixed film coated tablets as for FIG. 1 but with 8.3% TWG;

FIG. 5 shows the dissolution profile of tablets coated with 30% amylose: 70% Eudragit S at various polymer weight gains and Eudragit S coated tablets at 5% TWG;

FIG. 6 shows the dissolution profile of tablets coated with amylose 30% in pH 6.8 buffer; and

FIG. 7 shows drug release from tablets coated to 8.3% TWG in pH 6.8 buffer containing SOU/ml amylase.

Experimental

Preparation of Prednisolone Tablets

Prednisolone tablets (weight 200 mg, diameter 8 mm and standard bi-concave) were prepared according to the following formula: Lactose 85% Prednisolone 5% PVP 5% Ac-di-sol 4% (⅔ intragranular and ⅓ extragranunular) Magnesium stearate 1% (extragranular)

Prednisolone was dry mixed with the excipients and then wet granulated. Granules of 500-710 μtm size fraction were compressed using a single punch tabletting machine (Manesty, UK).

Formulation for Amylose Aqueous Dispersion Eurylon 7 16 g Butan-1-ol 32 g Water 352 g 

Eurylon 7 starch was dispersed well in the butan-1-ol and water subsequently added with good agitation. The resulting dispersion was then heated to boiling, and cooled with stirring overnight. The % solids content of the cooled dispersion was calculated based on the final weight of the dispersion (allowing for evaporation during heating).

Formulation for Eudragit S Solution

Eudragit S solution was prepared by dissolution of Eudragit S 100 polymer in 96% ethanol under high speed stirring. The final solution contained approximately 6% polymer solids.

Mixed Amylose-Eudragit Coating Dispersion

Appropriate quantities of the amylose dispersion and Eudragit solution were mixed to give the required ratios stated as the dry polymer substance. The amylose was always added to the Eudragit solution drop-wise under fast stirring. The resulting dispersions were left stirring for two hours before the addition of the excipients and for another two hours after adding excipients. The added excipients were: Triethyl citrate 10% of dry polymer substance Glyceryl Monostearate  5% of dry polymer substance

The final mixed polymer coating preparation was film coated onto the tablets using a fluidised bed spray coating machine. Coating thickness was estimated as % weight increase of the tablets following coating (% TWG)

The spray coating parameters were as follows: Flow rate 0.7 ml/minute Atomising pressure 0.2 bar Coating temperature 40° C.

In vitro Tests

Amylose dispersion was prepared from Eurylon 7, a high amylose starch, and mixed with a solution of Eudragit S in ethanol. The composition and preparation method for the coating dispersions are as described above. Various amylose/Eudragit S combinations were prepared containing 15%, 20%, 25%, 30% and 35% amylose. The mixed Eudragit/Amylose coating dispersion were then film coated onto prednisolone tablets prepared according to the method described above. Tablets were coated to varying thicknesses, calculated as total weight gain on the polymer, to also determine the optimum coating thickness. The coating mixture yielded good quality films up to a ratio of 30% amylose.

Coated tablets were then tested in vitro for drug release in varying pH buffer solution. The optimum amylose/Eudragit S ratio and coating weight gain was primarily based on comparison of the dissolution profile with conventional Eudragit S coated tablets.

Results are shown in FIGS. 1-7.

Very surprisingly these mixed film coated tablets were able to resist drug release in pH 1.2 HCl simulating the gastric media (see the left-hand side of the graphs of FIGS. 1-6).

In the small intestinal media, there was no drug release at pH 6.8 from any of the coated tablets for up to 12 hours (see FIG. 6). Previous in vitro studies using mixed amylose/acrylic polymers based on the water-insoluble Eudragit RL and RS showed uncontrollable swelling and rapid drug release in acid and buffer (Milojevic et al., 1996).

Drug release profiles from the coated tablets in pH 7.0 buffer media are shown in FIGS. 1-5. Based on the analysis of the dissolution profiles, tablets coated with a 30% amylose/Eudragit mixture to a film thickness equivalent to 8.3% was judged to be optimal, and were further tested to assess the digestibility of the amylose component of the film.

The tablets were dissolution tested in pH 6.8 buffer containing 50 U/ml ∝-amylase derived from B. licheniformis (see FIG. 7). A dissolution test was also carried out in pH 6.8 media with pancreatin to test whether the amylose is digestible by pancreatic α-amylase (see FIG. 6).

Results of the dissolution test in the presence of the enzymes show that the amylose component of the film is indigestible in the presence of the pancreatin (suggesting resistance in the small intestine), but drug release occurred within three hours in the presence of ∝ amylase from B. licheniformis. These results provide proof that the mixed film resists drug release in simulated conditions of the upper gastrointestinal tract but is digestible in the presence of bacterial enzymes (even at a pH lower than the threshold pH of the Eudragit S polymer for dissolution)

In vivo Study in Healthy Volunteers

Following the surprising success of the in vitro studies with the mixed amylose/Eudragit S film coated tablets; we sought to test the performance of the dosage form in healthy human subjects. The tablets were radio-labelled with Indium-111 and administered to eight healthy male volunteers on three separate occasions. The transit and disintegration site of the tablet in the gastrointestinal tract was followed using a gamma camera.

The time and site of disintegration of these mixed film tablets can be seen in Table 1. The results show surprisingly excellent colonic targeting, with tablet disintegration occurring primarily in the colon

The results from the healthy volunteer study provides proof that amylose and Eudragit mixed at a proportion of 30% amylose to 70% Eudragit S and coated onto tablets at approximately 8.3% TWG, is able to resist tablet disintegration in the stomach and small intestine but trigger disintegration in the colon.

This coating can be applied to a range of dosage forms, including tablets, capsules, pellets, granules etc.

Table 1 shows the site and time of disintegration of 30% amylose and 70% eudragit s coated tablets in eight healthy male volunteers on three separate occasions.

Key: Fasted=tablet given on an empty stomach

-   -    Partial fasted=tablet given on an empty stomach, but meal         administration 30minutes post dose     -    Fed=tablet given after breakfast

ICJ=ileocolonic junction; AC=ascending colon; HF=hepatic flexure; SF=splenic flexure. TABLE 1 Treatment 1 Treatment 2 Treatment 3 (Fasted) (Partial fasted) (Fed) Subject Site Time Site Time Site Time 1 ICJ 237 ICJ 244 AC 240 2 AC 200 ICJ 339 AC 316 3 AC 201 ICJ 350 AC 510 4 AC 292 HF 390 AC 415 5 TC 465 SF 678 AC 555 6 Subject did not — AC 523 AC 523 attend study day 7 AC 274 AC 244 SF 465 8 AC 614 Tablet did not — AC 455 empty from stomach

REFERENCES

Ashford, M., Fell J. T., Attwood, D., Sharma, H., and Woodhead, P (1993) An in vivo investigation into the suitability of pH dependent polymers for colonic targeting. Int. J. Pharm. 95: 193-199.

Basit, A. W. (2000) Oral colon-specific drug delivery using amylose-based film coatings. Pharm. Tech. Europe, 12(2): 30-36.

Bloor, J. R., Basit, A. W., Chatchawalsaisin, J., Fish, N. W., Newton, J. M., Wood, E. C., and Wilding, I. R. (1999) Colon targeting of ATL-2502 (Prednisolone sodium metasulphobenzoate) using COLAL™ coating, Pharm. Sci., 1 (4): S-453.

Dew, M. J., Hughes, P. J., Lee, M. G., Evans, B. K., and Rhodes, J. (1983) Colonic release of 5-aminisalicylic acid from an oral preparation in active ulcerative colitis. Br. J. Clin. Pharmacol., 16:185-187.

Gupta, V. K., Beckert, T., and Price, J. C. (2001) A novel pH and time-based multi-unit potential colonic drug delivery system. I. Development. Int. J. Pharm., 213: 83-91.

Milojevic, S., Newton, J. M., Cummings, J. H., Gibson, G. R., Botham, R. L., Ring, S. G., Stockham, M. and Allwood, M. C. (1996) Amylose as a coating for drug delivery to the colon: preparation and in vitro evaluation using glucose pellets. J. Control. Rel. 38: 75-84. 

1. A delayed release drug formulation comprising a particle with a core and a coating for the core, the core comprising a drug and the coating comprising a mixture of a first material which is susceptible to attack by colonic bacteria and a second material which has a pH threshold at about pH 5 or above, wherein the first material comprises at least one polysaccharide selected from the group consisting of starch; amylose; amylopectin; chitosan; chondroitin sulfate; cyclodextrin; dextran; pullulan; carrageenan; scleroglucan; chitin; curdulan and levan.
 2. A formulation as claimed in claim 1, wherein the polysaccharide is starch.
 3. A formulation as claimed in claim 1 or claim 2, wherein the polysaccharide is starch comprising at least about 0.1% amylose.
 4. A formulation as claimed in claim 3, wherein the polysaccharide is starch comprising at least 10% amylose.
 5. A formulation as claimed in claim 1 or claim 2, wherein the polysaccharide is starch comprising up to 100% amylopectin.
 6. A formulation as claimed in claim 1, wherein the second material is a film-forming polymeric material.
 7. A formulation according to claim 6, wherein the second material is an acrylate polymer.
 8. A formulation as claimed in claim 1, wherein the second material is an anionic copolymer of (meth)acrylic acid and (meth)acrylic acid C₁₋₄ alkyl ester.
 9. A formulation as claimed in claim 8, wherein the second material is an anionic co-polymer of methacrylic acid and methacrylic acid methyl ester.
 10. A formulation as claimed in claim 9, wherein the ratio of methacrylic acid to methacrylic acid methyl ester is about 1:2.
 11. A formulation as claimed in claim 1, wherein the second material is Eudragit® S.
 12. A formulation as claimed in claim 8, wherein the second material is a copolymer of methacrylic acid and ethyl acrylate.
 13. A formulation as claimed in claim 1, wherein the second material is a cellulose polymer or a polyvinyl-based polymer.
 14. A formulation as claimed in claim 13, wherein the cellulose polymer is cellulose acetate phthalate; cellulose acetate trimellitate; or hydropropylmethylcellulose acetate succinate.
 15. A formulation as claimed in claim 13, wherein the polyvinyl—based polymer is polyvinyl acetate phthalate.
 16. A formulation as claimed in claim 1, wherein the proportion of the first material to the second material is up to about 35:65.
 17. A formulation as claimed in claim 16, wherein the proportion of the first material to the second material is from 15:85 to 35:65.
 18. A formulation as claimed in claim 1, wherein the minimum diameter of the particle is at least about 5×10⁻⁴ m.
 19. A formulation as claimed in claim 1, wherein the thickness of the coating as measured by theoretical weight gain of the coated formulation is from 5 to 10%.
 20. A formulation as claimed in claim 1, wherein the thickness of the coating as measured by theoretical weight gain of the coated formulation is from 15 to 35%.
 21. A formulation as claimed in claim 1, wherein the coating has a thickness of from about 10 μm to about 150 μm.
 22. A formulation as claimed in claim 1, wherein the drug comprises at least one acidic group.
 23. A formulation as claimed in claim 1, wherein the drug is an anti-inflammatory agent.
 24. A formulation as claimed in claim
 22. wherein the drug is 5-aminosalicylic acid.
 25. A formulation as claimed in claim 1, wherein the drug is a steroid.
 26. A formulation as claimed in claim 25, wherein the drug is selected from prednisolone; budesonide; fluticasone and derivatives thereof.
 27. A formulation as claimed in claim 1, wherein the drug is an antineoplastic agent. 28-31. (canceled)
 32. A method of treating inflammatory bowel disease comprising administering to a patient in need of such treatment a therapeutically effective amount of a formulation as defined in claims 23, 24, 25, or 26 to treat the inflammatory bowel disease.
 33. A method of treating carcinoma comprising administering to a patient in need of such treatment a therapeutically effective amount of a formulation as defined in claim 27 to treat the carcinoma.
 34. (canceled)
 35. A method of preparing a delayed release drug formulation as claimed in claim 1, said method comprising: forming a core comprising a drug; and coating the core with a polymer coating preparation comprising a mixture of a first material which is susceptible to attack by colonic bacteria and a second material which has a pH threshold at about pH 5 or above, wherein the first material comprises at least one polysaccharide selected from the group consisting of starch; amylose; amylopectin; chitosan; chondroitin sulfate; cyclodextrin; dextran; pullulan; carrageenan; scleroglucan; chitin; curdulan and levan.
 36. A method as claimed in claim 35, which comprises spray coating the core with said polymer coating preparation.
 37. A method as claimed in claim 35 or claim 36, comprising: forming an aqueous dispersion of said first material; forming an alcoholic or aqueous solution of said second material; and adding at least a portion of said aqueous dispersion of said first material to at least a portion of said alcoholic or aqueous solution of said second material to form said polymer coating preparation.
 38. A method of targeting a drug to the colon of a patient comprising administering to the patient in need of such treatment a formulation as claimed in claim
 1. 39-41. (canceled) 